$($a$)$ XYZ welfare group is a new investment team specializing on the returns from the Financial Assets Investments. Being their first time to venture in this area, the group very cautious in the investment choice. The leaders have approached you for professional advice on the building blocks of a good financial forecast. Advice. $(8$marks$)$

$($b$)$ The following data have been recorded for sales over the last four years

$\backslash$table$[[$Sales in thousands of units,$],[$Year $1,70,32,55,60],[$Year $2,65,29,50,58],[$Year $3,76,43,58,62],[$Year $4,83,54,65,71]]$

Using the Additive Time Series model,

Required